Art of drying



G. D. HARRIS ART OF DRYING Filed Oct. 20, 1922 Nov. 24, 1925- PatentedNov. 24, 1925. v

GORDON DON HARRIS, OF FREEEPORT, EW YORK, ASSIGNOR, BY MESNE ASSIGN-MENTS, TO THE INDUSTRIAL DRYER CORPORATION, OF STAMFORD, CONNECTICUT,

A CORPORATION or CONNECTICUT.

ART OF DRYING.

Application filed October 20, 1922. Serial 1%. 595,747.

To-aZZ whom it may concern."

Be it known that I, GORDON Don HARRIS, a citizen of the United States,residing at Freepo rt, county of Nassau, and State of 5 New York, haveinvented a certain newand useful Art of Drying, of which the followingis a specification. Preliminary to drying certain materials, such aswood, it is desirable, by tests, to determine certain physicalcharacteristics of said material, such as the water content thereof, andthe rate at which the contained water spreadsor diffuses through thefibres, and within said material, in'order for the body of the material.s M In the process of drying wood, it is known that as the containedwater within the material decreases, due to surface evaporation,

the spreading or diffusing of the water content becomes slower, and,further, that such spreading and diffusing of the water content does nottake place uniformly throughout the mass of the material, this unequal.

spreading in the case of wood being due to a natural physical formationof the material, as well as the presenceof oneor more inherentconstituents of such material. a result of the unequal diffusion of themoisture content within the material, there occurs, at regular orirregular stages of the drying period, a dry surface on the material, i.e., a surface free or substantially free from moisture, an when heat issteadily areas by the flow of a drying atmosphere into continued contacttherewith, it follows that such application of heat tosuch .dry

areas, attaining the undesirable condition known as case hardening.

With a View to the economical and prac: ticaldrying'of materials of thatcharacter wherein the diffusion of the water content takes placeirregularly and unequally, the

water content to reach the surface of thesupplied for a certain periodto such dry- PATENT OFFICE.

process of drying-is required to be controllabl e at will with a View toso conditioning .the drying atmosphere at different stages that suchatmosphere is suited to the condition of the material. In thisinvention, the process is based upon a physical law demandingequalization of two bodies of different densities, one of such bodies,in this instance, being the material with a known moisture content andwith a givenorate of diffusion of such content, and the other body beinga drying atmosphere with a determined, although controllable, humidityand temperature.

Accordingly, the drying atmosphere flowing into contact with materialplaced within a closed chamber is controllable as regards both thetemperature and'humidity of such atmosphere, at any and all stages ofthe evaporation, to the end that the temperature can range from high tolow, or vice versa, together with the control of the humidity of suchatmosphere to attain different percentages of moisture contentthroughout the drying period, whereby the atmosphere is suited atdifferent stages in the drying operation to correspond with variationsin thewatercontent of the material, and particularly to the surfacecondition, either wet or dry, .of the material undergoing treatment.

Obviously, the humidity of the atmosphere is, or should be, constantlyless than the moisture present on the surface of the material, to. theend that the atmosphere performs with efficiency the elimination of suchsurface moisture, but at certain stages in the evaporation of moisturefrom the material, there occurs on the surface of such material adrycondition, i. e., an area sub stantially free a from surface moisture,so that the humidity of the atmosphere 1s of greater density than thedry area of the material, and at this stage'in the treatment of thematerial the action is reversed to the end that moisture present in theatmosphere is depositedupon the dry surfaces of the material, the effectof which is to moisten the dry area of the material by the humiditycarried by the atmosphere, such deposit of moisture from atmosphere tomaterial taking place for an indeterminate period and density of suchatmosphere is conditioned with reference to the surface moisture of thematerial and the rate of diffusion of the water content within the massof such material, to the end that there may be prac tically obtainedthat condition which meets the requirements with respect to theequalization of two' bodies of different densities. During the progressof the evaporation, the

- moisture content of the material decreases,

the moisture exuding to the surface of the material and being carriedaway from. the presence of such surface by the flow of the atmosphere.As the moisture content of the material decreases, the atmosphere isconditioned by increasing or decreasing its temperature and the humidityis varied in a certain ratio to such decreased moisture content on thesurface of the material, and also to the rate of diffusion within thematerial, having in- View, however, the'presence of such percentage ofhumidity in the atmosphere as will result in the deposit of moistureupon the dry areas, so called, produced. upon the surface of thematerial by the absence of moisture occasioned by an inequality in thediffusion of such moisturewithin the mass of the material itself, due

..to the physical formation or the inherent resinous content of suchmaterial.

The evaporatlon is conducted wlthin-a chamber: closed to the admissionof outside atmospheric air, and the control of the atmosphere within thechamber is obtained by heaters and condensers, said heaters andcondensers being positioned in different zones within a circulatory pathfor such atmosphere, whereby the heaters act to impart to the atmospherethe heat units required to efl'ectuate the evaporation as well as toproduce the required upflow into contact with the material, whereas thecondensers act upon the atmosphere for the dual purpose of chilling suchatmosphere to insure its downflow within a definite part of thecirculatory path and to condense a certain portion of the aqueouscontent of such atmosphere, which condensation eliminates to asubstantial and determined degree that moisture taken up by the airfromthe material in the exchange of heat for moisture.

The process is carried out in various forms I of apparatus, one of whichis diagram- .other end of said chamber.

matically illustrated in vertical sectional elevation in theaccompanying drawing.

H, The material, in the form of lumber, is stacked or piled upon atruck, B, which is introduced with the load into a chamber, A,

referred to as a drying chamber, the same constituting a part of acirculatory path closed against the admission of outside atmosphericair, and through which chamber and the stacked material flows a dryingatmosphere adapted to be expanded by an initial heater, C. As shown, theatmosphere flows within a bottom flue, 0, within which is positioned theinitial heater, shown as coils to which steam is supplied through apipe, 0, controlled by a valve, 0. Connected to the bottom flue is anupdraft flue, D,

and a down-draft flue, E, said updraft flue, K

D, being at one end of the drying chamber, whereas a similar updraftflue, D, is at the These updraft flues are shownas having dampers, d, d,positioned in such relation to the drying chamber and to the flues thatthe atmosphere is directed to flow from the initial heater flue, G, intoa part of flue, D, thence into the lower art of the drying chamber andthrough the stacked material therein, thence into the lower part offlue,

D, thence back to the drying chamber on a' level above the first flow ofthe atmosphere therein, thence into the upper part of flue, D, backagain through the drying chamber,

and thence into the down-draft flue, E.

The atmosphere flowing into contact with the initial heater, C, isheated to the tem perature required to effect the evaporation ofmoisture from the material within the chamber, A, i. e., the atmospherecarries the required heat units to so act on the material asto exchangeheat for moisture, and during this flow of the atmosphere within thedrying chamber it is conducted and deflected into the required contactwith all surfaces of the material, thus carrying out the evaporationstage of the process. During theexchange of heat for moisture, the airgives off a certain proportion of the heat units and its temperature isreduced, but to attain efficiency in the evaporation at all stages ofthe process, I employ compensating heaters, F, which are positionedwithin the flues, D,,D, and in the line of flow of the atmosphere, suchheaters being shown as having sources of steam supply through pipes, 7,provided with controlling valves. 7", as usual. The temperature of theatmosphere as it makes the passes into contact with the material isindicated by one or more thermometers, the position of one of which isindicated at G, in the upper part of flue, D. Obviously, a drop in thetemperature of the atmosphere due to the exchange of heat for moisturewill be indicated by the thermometers, but by opening the moisture tendsto decrease the temperature of the atmosphere, but by using compensatingheaters within the line of flow of the atmosphere, andby controllingsaid com pensating heaters, the heat units radiated are apportioned to adecrease in the water content evaporated from the material undertreatment.

The atmos here flowing within the drying chamber an into contact withthe material thereiIr attains a certain moisture content and acquires aparticular or specified moisture load prior to flowing, into the down,

draft flue, E, and at this stage in the flow of the atmosphere it isbrought into contact with a condenser or condensers, H, the same havingthe capacity for chilling theatmosphere to a specified dew point, theeffect of which is to depositall water vapor in excess of a specifieddew oint. As shown, the condenser, H,'is a c oi positioned within thedown draft flue, E, and adapted to be supplied with a cooling agent,such as cold water, brine, or ammonia, through pipes, it, provided withcontrolling valves, It The condensate deposited upon the condensingcoils is free to drop into a collecting trough, I, with a valveddischarge, z', ,leading to the exterior of the apparatus.

The humidity of the atmos here descending within the flue, E, is inicated by the dew point made as indicated by the thermometer, theposition of which is denoted at J, but the chilling of the atmosphereand the condensation of moisture is controllable by varying the volumeor character of the cooling agent supplied to the condenser, H, to theend that the humid condition of the atmosphere is controllable by thedeposit of a specified quantity of water vapor upon the condensers, thusestablishing and maintaining a desired moisture content of theatmosphere in proportion to the surface moisture present on thematerial, although as the evaporation progresses, such humid conditionof the atmosphere may be controlled to attain a decreased or increasedmoisture content in proportion to the decrease in the moisture contentof the material.

- The mode of (procedure is apparent from the foregoing escri ption, werein it apor series of-coils,

pears that material is loaded on the truck and deposited within thechamber, the same being closed tightly against. the ingress of outsideatmospheric air. Steam is supplied to the initial heater for raising theatmosphere to the desired temperature, and expanding such atmosphere tocreate the flow within chamber A, and into contact with the materialtherein. The atmosphere is directed to all surfaces of the material toeffect the the exchange of heat for moisture, with the attendant ratioloss of heat, the compensating heaters, F, are brought into service witha view to radiating heat ,in the same ratio or proportion as that lostby the evaporation, to the end that the temperature remains constant,the effect of which is to establish "5 eva oration and at the 1'6 uiredsta e 7 I:

and maintain a specified temperature in all parts of the drying chamber.The atmosphere makes a number of passes within the chamber and intocontactwith the material, so as to acquire a specified water vapor load,

and thence passes out of the chamber and into flue, E, the condensers inwhich cool or chill the atmosphere to eflect the downflow within theflue, E, whereby the atmosphere is chilled to a specified dew pointandthus deposits upon the condensers all water vapor in excess of thespecified dew point.

It is this apparent that by, expanding theatmosphere and cooling suchatmosphere that a circulation is set u within the closed path to theexclusion of t e outside air, and it is thus possible,- byheating theair to a required temperature and by chilling the,

atmosphere to a specified dew point, to so condition the atmosphere inrespect to both its temperature and humidity as to apportionsuchatmosphere to the water content and surface moisture of the material andthe rate of difiusion or spreading of such 7 water .content within themass of such material, the result of which is to equalize the actionof'the two bodies of different densitieS.

The process described attains economy for the reason that a containedvolume of atmospheric air within a closed path is utilized for conveyingtheheat units to the roduct under treatment, and this same vo ume of airis used as the agency for conveying the temperature and humidity suitedto attain eva oration of moisture 'from the material without im airingthe character or physical structure 0 such material.

Although reference has been made to the -water vapor out of the presenceof the matetreatment of wood for evaporating water therefrom, it .willbe understood that my process is useful in the treatment ,of differentkinds of material.

Having thus fully described the invention, what I claim as new anddesire to secure by Letters Patent is:

1. In the art of drying, the process which consists in setting up theflow of an atmosphere within a closed circulatory path by alternatelyheating and cooling such atmosphere, and condensing a certain percentageof the aqueous content of such atmosphere at the chilling stage thereof,for controlling the humidity of such atmosphere in a definite proportionto the-surface moisture of the material under treatment.

2. In the art of drying, the process which consists in setting up theflow of an atmosphere within a closed path by alternately heating andchilling such atmosphere, condensing some of the aqueous content of suchatmosphere and thereby controlling the humidity thereof in a definiteproportion to the surface moisture of the material, under treatment, andheating such atmosphere for. maintaining a constant temperature in theperiod of its flow between the initial heating and the subsequentchilling thereof.

3. In the'art of drying, the process which consists in setting up theflow of an atmosphere within a path closed to the exclusion of outsideair by initially heating and subsequently cooling such atmosphere,condensing some of the aqueous content ofsuch atmosphere at' thechilling stage thereoffor controlling the humidity of such atmosphere ina definite ratio to the surface moisture of the material undertreatment, and heat ing the atmosphere to a constanttemperature in theperiod of its flow between the initial heating and the subsequentcooling thereof.

4. In the art of drying, the process which consists in initially heatingand subsequently chilling a drying atmosphere to set up the flow of suchatmosphere into contact with material, and controlling the humidity ofsuch atmosphere by condensing the aqueous content thereof in a definiteratio to the surfhce'moisture of suchmateriah 5. In the art of drying,'the process which consists in initially heating and subsequentlychilling a drying atmosphercfito set up the flow of such atmosphere intocontact with material, and controlling the humidity of such atmosphereby condensing some of the aqueouswontent thereof in a definite ratio toa decrease in the surface moisture of such material.

6. In the art of drying, the process which consists in initially heatingand subsequently cooling the atmosphere to set up a flow of suchatmosphere into contact with material, condensing the aqueous content ofsuchatmosphere to a definitedewpoint for controlling the humidity ofsuch atmosphere in proportion to the surface moisture'of the materialand to its diffusion within such material, and heating such atmosphereto a constant temperature in the periods between its initial heating"and the subsequent cooling thereof.

In testimony whereof, I have hereunto signed this specification at theState of New York, this 13th day of October, 1922.

eonnon 1'). HARRIS.

